The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty
The invention relates to implantable articles and methods for manufacturing such articles. More importantly, the invention relates to bone prosthesis, bone prosthesis instrumentation and processes for manufacturing the same.
There are known to exists many designs for and methods for manufacturing implantable articles, such as bone prosthesis. Such bone prosthesis includes components for artificial joints, such as elbows, hips, knees and shoulders. An important consideration in the designing or manufacturing of any implantable bone prosthesis is that the prosthesis has adequate fixation when implanted within the body.
Earlier designs of implantable articles relied upon the use of cements, such as polymethylmethacrylate (PMMA) to anchor the implant. The use of such cements can have some advantages, such as providing a fixation that does not develop free play or does not lead to erosion of bone faces post-operatively. However, the current trend is to use these cements to a lesser extent because of their tendency to lose adhesive properties over time and the possibility that the cement contributes to wear debris within the joint. When utilizing these cement implants, the implants are designed to be smaller than the respective cavity. The implant is placed in the cavity and a mantel or layer of cement is applied between the cavity and the implant.
Recently, implantable bone prosthesis have been applied and designed such that they encourage growth of hard tissue (ie. bone) around the implant. The bone attachment usually occurs and growth is promoted when the surface of the implantable bone prosthesis is irregular or textured. The bone attachment usually occurs and growth is promoted when the surface of the implantable bone prosthesis has been found to provide a good fixation of the prosthesis with the body. A greater degree of bone fixation interaction of newly formed hard tissue in and around the texture can usually be achieved when bone-engaging surfaces of an implantable bone prosthesis are more porous or regular. For prostheses designed to encourage bone in-growth, the cavity into which the prosthesis is implanted closely conforms to the periphery of the bone prosthesis. Such bone prostheses are press-fitted into the bone cavity.
One of the considerations as to whether to use a cemented stem or a pressed-fitted stem in a prosthetic joint implant is the overall health or condition of the patient""s bone. Long bones, particularly the femur, are typically classified into three general classifications of bone structure. These classifications are related to the health of the bone. The health of the bone is typically attributable to the progression of disease within the long bone. The typical long bone diseases that lead to total hip arthroplasty are ostoarthritis, avascular necrosis, and rheumatoid arthritis.
The three distinct classifications of bone structure of the femur can be identified between the metaphysis and the diaphysis. These three types of bone structures are type A, type B, and type C bone structure. These types of bone structure are more fully described in an article by Dorr, L D., Faugere, M C., Mackel, A M., Gruen, T A., Bogner, B., Malluche, H H. xe2x80x9cStructural and Cellular Assessment of Bone Quality of Proximal Femur.xe2x80x9d Bone 1993: 231-242 hereby incorporated by reference in its entireties.
In Type A bone structures thick medial and posterior cortices are evident. They begin at the distal end of the lesser trochanter and are quite thick immediately. This creates both a narrow diaphyseal canal and a funnel shape to the proximal femur. The thicker cortices and less porosity result in a lower canal to calcar isthmus ratio. This type of bone is found more often in younger patients.
In Type B bone structures both the medial and posterior cortices exhibit bone loss. The medial cortex is thinned compared to Type A bone but a funnel shape is still present. The funnel shape of the canal remains good for implant fixation. The posterior cortex is especially thinned, or absent, and causes the width of the intramedullary canal to increase. The shape of the bone is proportional at the top and bottom.
In Type C bone structures the bone has lost nearly all the medial and posterior cortices, which result in a xe2x80x9cstovepipexe2x80x9d shape of the intramedullary canal. It has the thinnest cortices of the 3 types of bone, a wide intramedullary canal, and appears somewhat xe2x80x9cfuzzyxe2x80x9d in x-rays. This type of bone is seen most often in older patients.
Cemented implants are more often used in patients with the type C bone structure, while cementless implants are more commonly used in patients with type A bone structure. Further, in many cases cemented implants are used in cases where the ratio where the proximal canal width to the distal canal width is less than the ratio for cases in which the cementless implants might be used.
Stem components for total joint arthroplasty typically have a wedge shape with the distal portion of the stem being smaller in cross section than the proximal cross section. Typically, the stem has a continually decreasing cross-sectional area in the direction from the proximal portion to the distal portion of the stem.
Due to the differences in the types of bone for which the cemented and cementless stems are designed, the shapes of the stems vary widely from one type of prosthetic stem to another. As mentioned before, some cemented stems have a larger difference between the cross-sectional area or width of the proximal portion of the stem to the distal portion of the stem.
Cemented and uncemented stems are implanted into a canal or cavity prepared in a resected long bone. The cavity in the long bone may be prepared utilizing at least one of several types of instruments. For example, the cavity may be prepared by a drill, reamer, or broach. A hip stem cavity may typically be prepared by a combination of drilling, reaming, and broaching. The broaching includes teeth or cutting edges which remove material from the bone. The broach generally has a shape equal to the shape of the stem.
In order to prepare a cavity for a particular stem, a unique broach with a unique profile must be available for preparing that cavity. Even for a particular stem, the surgeon may have patient-specific reasons or general-practice preferences for a cement mantel or thickness of the cement along the profile of the stem which may be different than that provided by the manufacturer of the stem and accompanying broaches. Thus, the prior art requires a vast number of broaches, namely, one for each particular size of a particular design of stem. And even with such a variety of stems, the configuration of a broach limits the surgeon to one particular cement mantel pattern for a particular hip stem and hip stem broach combination.
According to the present invention, an orthopedic implant tool includes a feature which permits a portion of the periphery of the instrument to be adjustable so that the tool may prepare more than one type of cavity for an orthopedic implant stem. The tool could be expanded or contracted to accommodate either a type A or a type C bone structure. Preferably, the expansion or contraction of the instrument is done in a controlled fashion such that a plurality of different feature sizes could be accommodated by one particular instrument.
The adjustable instrument permits the ideal sizing of the cavity for a particular implant. The adjustable instrument is able to replace separate instrument sets for cemented and cementless implants and reduces both cost and complexity for the manufacturer and the consumer of the instruments.
The present invention allows the same instrument or broach to create an envelope more conducive to the anatomical femur shape via either type A, type B, or type C bone structure and allows the implant to be ideally designed accordingly.
The adjustable instrument may be used for the reconstruction of any joint in which the intermedullary space of the long bone is prepared for a prosthesis. For example, the adjustable instrument may be utilized for shoulders, elbows, hips, and knees, as well as wrists and ankles. The adjustable instrument allows for the optimally designed cemented and cementless implants to fit into the operable broach envelope created by a single set of broaches.
According to one embodiment of the present invention, a tool for preparation of a cavity in a long bone for receiving a joint prosthesis for use in arthroplasty is provided. The tool includes a body having an outer periphery of the body. The outer periphery is adapted to have a first shape and a second shape of the body. The second shape has dimensions different than the first shape. The tool, when in the first shape, is capable of forming a first cavity in the long bone; and the tool, when in the second shape, is capable of forming a second cavity in the long bone. The second cavity is different than the first cavity.
According to another embodiment of the present invention, a hip joint prosthesis for cooperation with a long bone for use in arthroplasty is provided. A cavity is formed in the femur. The prosthesis includes a stem having portions of the stem for placement at least partially within the cavity of the femur. The stem defines a longitudinal axis of the stem. The prosthesis also includes a bearing for placement in the cavity between the stem and the femur so that the distal portion of the stem is spaced from the femur.
According to yet another embodiment of the present invention there is provided a broach for removal of bone for preparation of a cavity in a long bone for receiving a joint prosthesis for use in arthroplasty. The broach includes a body having an outer periphery of the body. At least portion of the body is capable of being flexed so that the outer periphery may have an expanded shape and a contracted shape of the body. The contracted shape has dimensions different than the expanded shape, whereby the tool when in the expanded shape is capable of forming a first cavity in the long bone; and the tool, when in the contracted shape, is capable of forming a second cavity in the long bone. The second cavity is different than the first cavity.
According to another embodiment of the present invention, an instrument kit for use in total joint arthroplasty is provided. The kit includes a broach for removal of bone for preparation of a cavity in a long bone for receiving a joint prosthesis. The broach includes a body having an outer periphery of the body. At least a portion of the body is capable of being flexed so that the outer periphery may have an expanded shape and a contracted shape of the body. The contracted shape has dimensions different than the expanded shape. The broach, when in the expanded shape, is capable of forming a first cavity in the long bone; and the broach, when in the contracted shape, is capable of forming a second cavity in the long bone. The second cavity is different than the first cavity.
According to a further embodiment of the present invention, a method for performing total joint arthroplasty comprising the steps of determining the appropriate implant stem to implant into the long bone, determining the appropriate size of cavity to prepare in the long bone, based on the size of the appropriate implant stem to implant, providing a broach having cutting path size adjustment capabilities, adjusting the cutting path size of the broach based on the appropriate size of cavity to prepare in the long bone, preparing a cavity in the medullary canal of a long bone with the broach, and installing the stem in the cavity of the long bone is provided.
The technical advantages of the present invention include the ability to customarily adjust the shape of the cavity for a prosthetic stem. For example, according to one aspect of the present invention, an instrument in the form of a broach includes a portion thereof which is expandable or contractible so that a portion of the broach may be enlarged or reduced to change the shape of the broach. Thus, the present invention provides for an adjustable customized cavity for a prosthetic stem.
Another technical advantage of the present invention includes the ability to replace a series of fixed broaches with a single adjustable broach. For example, according to one aspect of the present invention, the broach includes an adjustment feature such that the broach may be set in one of a series of different dimensions, each dimension corresponding to one a set of otherwise fixed broaches so that the adjustable broach can replace a plurality of fixed broaches. Thereby, the present invention replaces a series of broaches with a single broach.